Engine ignition systems may include a spark plug for delivering an electric current to a combustion chamber of a spark-ignited engine, such as a gasoline engine, to ignite an air-fuel mixture and initiate combustion. Spark plug fouling may occur wherein a firing tip of the spark plug insulator becomes coated with a foreign substance, such as fuel or soot. Soot-fouled spark plugs include a carbon build-up on an electrode of the spark plug, whereas wet-fouled spark plugs include liquid fuel build-up around the electrode. Spark plugs may become wet-fouled due to engine flooding, for example. The engine may flood due to rich fueling during extreme temperature weather conditions, when an operator depresses/pumps the gas pedal repeatedly during cranking, or due to excess fuel inside the cylinders (e.g., due to a degraded fuel injector). When the spark plugs become wet-fouled, they are unable to produce a spark across the electrode, thus delaying or preventing engine start. In some instances, engine flooding may cause a frustrated vehicle operator to continue cranking the engine until the battery drains. Further, vehicle emissions may be increased due to repeated unsuccessful cranks while the engine is flooded.
Other attempts to address spark plug wet-fouling include methods for removing fuel adhered to the spark plug while the spark plug remains in the engine. One example approach is shown by Ayame et al. in U.S. Pat. No. 7,523,744 B2. Therein, a method is disclosed that cranks the engine without injecting additional fuel in response to an indication that the engine has not started properly (e.g., within a duration of beginning the cranking).
However, the inventor herein has recognized potential issues with such systems. As one example, cranking the engine without providing additional airflow to dry the spark plugs may be inefficient, resulting in increased engine starting times. The increased engine starting times may increase vehicle operator frustration as well as consume excess battery charge. Further, the inventor herein has recognized that different vehicle systems may be utilized to provide the additional airflow based on a configuration of the vehicle and/or operating parameters. As one example, some engine systems may be configured with one or more boosting devices, such as turbochargers or superchargers, to increase airflow into a combustion chamber. Turbochargers and superchargers compress intake air entering the engine using an intake compressor. While a turbocharger includes a compressor that is mechanically driven by an exhaust turbine, an electric supercharger includes a compressor that is electrically driven by a motor. Therefore, the electric supercharger may be used to provide on-demand airflow. As another example, some engine systems may be configured with an evaporative emissions system that includes a pump operable in a positive pressure mode in which air is drawn into the evaporative emissions system from the atmosphere. As such, the pump of the evaporative emissions system may also be used to provide on-demand airflow. As still another example, some engine systems may include both the electric supercharger and the evaporative emissions system including the pump.
In one example, the issues described above may be addressed by a method comprising: in response to flooding a combustion chamber of a spark ignition engine with fuel during an engine start attempt, shutting off fuel delivery to the combustion chamber and directing compressed air from an electrically driven compressor through the combustion chamber under predetermined conditions prior to a subsequent engine start attempt. In this way, on-demand airflow may be provided by the electrically driven compressor to dry a wet-fouled spark plug coupled within the combustion chamber, thereby reducing engine starting times and decreasing vehicle emissions.
As one example, such as when an evaporative emissions system having a pump operable in a positive pressure mode is fluidically coupled to an intake of the engine, the predetermined conditions may include a load of a fuel vapor storage canister of the evaporative emissions system being greater than or equal to a threshold load. For example, the method may include selecting between directing the compressed air from the electrically driven compressor and directing air from the evaporative emissions system through the combustion chamber based on the load of the fuel vapor storage canister. As another example, air (e.g., provided by the electrically driven compressor or the evaporative emissions system) may be directed through the combustion chamber while the engine is at rest, such as by positioning the engine with an intake and an exhaust valve of the combustion chamber open via an electric motor, or while the engine is continuously spinning via the electric motor. The method may include selecting between flowing the air through the combustion chamber while the engine is at rest and while the engine is continuously spinning based on a state of charge of a system battery. For example, flowing the air through the combustion chamber while the engine is at rest may be selected when the state of charge is less than a threshold state of charge, and flowing the air through the combustion chamber while the engine is spinning may be selected when the state of charge is greater than or equal to the threshold. By flowing the air through the combustion chamber while the engine is spinning while the state of charge is greater than or equal to the threshold state of charge, engine starting times may be decreased compared with flowing the air through the combustion chamber while the engine is at rest, whereas by flowing the air through the combustion chamber while the engine is at rest, battery consumption may be decreased compared with flowing the air through the combustion chamber while the engine is spinning. Overall, wet-fouled spark plugs may be dried faster than when no additional airflow is provided, decreasing the engine starting times and thereby decreasing vehicle operator frustration.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.